1. Field of the Invention
The present invention relates to static hazard detection technology that checks whether there is a possibility of a static hazard occurring at a logic circuit synthesized by a logic synthesis tool.
2. Description of the Related Art
In LSI design, a signal referred to as a control signal is introduced in order to control the propagation of an exception signal such as a multi-cycle signal or an asynchronous signal that is not propagated between registers within one clock signal period. A control signal is a signal that is in a first state (for example, ‘1’) when it is acceptable to take in an exception signal and is in a second state (for example, ‘0’) when taking in of an exception signal is not acceptable. For example, propagation of an exception signal can be controlled by taking an AND (logical product) of a control signal and an exception signal or by controlling a selector that selectively outputs the exception signal and other signals using a control signal. There are also cases where the control signal is referred to as a strobe signal.
However, there are also further cases where circuits are created that generate glitches as a result of unexpected synthesis by a logic synthesis tool regardless of a designer writing HDL (Hardware Description Language) intended for a circuit for controlling propagation of an exception signal using a control signal. This means that control using the control signal is no longer effective and that the circuit operates erroneously. This problem is referred to as a static hazard.
Static hazards cannot be identified at the RTL (Register Transfer Level) stage. It is therefore necessary for an inspector to check for the occurrence of a static hazard by visually examining and analyzing the circuits generated by the logic synthesis tools individually. This method requires an enormous number of steps however, and there is still a danger of a static hazard going undetected.
On the other hand, technology is disclosed in, for example, Unexamined Japanese Patent Application KOKAI Publication No. 2006-323727, for detecting logical blocks where it is possible that glitches have occurred. In Unexamined Japanese Patent Application KOKAI Publication No. 2006-323727, technology is disclosed where paths are searched for two signals designated within the logic circuit. Logic blocks that propagation signals for the two signals are inputted to are then detected. This enables logic blocks where the occurrence of glitches is possible to be detected. Two asynchronous signals (exception signals) are specified as the two signals.